This invention relates to a fuel injection apparatus for an internal combustion engine and more particularly to an improved control arrangement for a fuel injection arrangement.
In fuel injected engines, it is, of course, extremely important to accurately control the quantity of fuel injected in accordance with the air inducted in order to achieve the optimum fuel/air ratio for a given operating condition of the engine. Various devices have been proposed for measuring the air flow in an induction system of an engine to control the amount of fuel injected. Conventionally, such air flow measuring devices have been large and complicated, and have been positioned in the induction system, normally upstream of the point of discharge of the fuel. In one type of flow detector, a flap type arrangement is provided in the intake passage and has a member that swings open to an amount that is determined by the air flow. The angular position of this detector is then measured and used to provide an air flow signal for the fuel injection system. Alternatively, vortex type air flow meters have been positioned in the induction system for determining air flow. Still another type of measuring device employs a hot wire anemometer which provides an electrical resistance wire interposed in the air stream to have its resistance vary in relation to the speed, i.e., cooling effect, of the air flowing through the induction system. The use of such flow meters in the induction system has several disadvantages.
In the first instance, the provision of an air flow measuring device in the induction system can oftentimes reduce the volumetric efficiency of the induction system. Furthermore, such devices substantially increase the size of the induction system. Also, devices of the type aforementioned are not particularly efficient with engines having a low number of cylinders or specifically with single cylinder engines due to the pulsations in the intake flow. Although such pulsations may be reduced to some extent through the use of a plenum chamber, this adds still further to the size of the induction system. Furthermore, if the flow meter is used in conjunction with the internal combustion engine of an outboard motor or other marine application, there is a high likelihood of corrosion in the moving components of the flow meter due to the salt in the atmosphere.
In U.S. Pat. No. 4,446,833 to Matsushita et al., and assigned to the assignee hereof, there is disclosed a control for a fuel injection system that has none of the foregoing disadvantages. The system disclosed in that patent senses the pressure in the crankcase of a two-cycle engine and uses the sensed pressure to control the amount of fuel injected. It has been found that the pressure in the crankcase is, if accurately measured, indicative of the amount of air inducted.
Although the arrangement shown in the '833 patent is particularly effective in controlling the amount of fuel injected without the disadvantages of the above-discussed air flow measuring devices, there are some instances when the crankcase pressure is not actually related to the amount of air inducted. For example, with two-cycle crankcase compression engines it has been found that the peak pressure immediately prior to the piston reaching bottom dead center is abnormally raised when the transfer or scavenge port is open due to the back flow of exhaust gases into the crankcase. As noted earlier, one desirable method for controlling the amount of fuel injected involves sensing both the minimum and maximum pressures in the chamber. However, since the maximum pressure is abnormally high due to the opening of the scavenge port and the back flow of exhaust gases, such a control arrangement is not as accurate as it might otherwise be.
Japanese Provisional Patent Publication Sho59-5875 discloses an engine wherein the air intake amount, for determining a proper amount of fuel for injection, is determined by making two separate pressure measurements during each crankshaft rotation. A value for the air intake amount is obtained by measuring the air pressure near the scavenging port opening timing, which is representative of the mass of the air remaining in the crank chamber at the beginning of the scavenging stroke; and, also, measuring the air pressure near the scavenging port closing timing, which is representative of the mass of the air remaining in the crank chamber at the termination of the scavenging stroke.
As discussed above, however, and particularly during low load, low speed operation, pressure from the combustion chamber may affect the pressure in the crank chamber when the scavenging port is opened. Thus, a temporary rapid rise in pressure may take place within the crank chamber. When this occurs, employing the crank chamber pressure value for determining the mass of the air inducted therein may cause a significant error in the value of the air intake amount calculated therefrom, which would result in decreased accuracy in arriving at the proper amount of fuel injection required.
It is, therefore, a principle object of this invention to provide an improved fuel flow control arrangement for the fuel injection system of an engine.
It is another object of this invention to provide an improved air flow measuring system of an internal combustion engine that accurately controls fuel flow in response to the amount of air flowing through the intake system.
It is yet a further object of this invention to provide a fuel control for a fuel injection system that does not rely upon a device that is interposed in the air induction system.
It is still a further object of this invention to provide a fuel injection system that senses differences in crankcase pressure and which eliminates the effects of abnormal changes in crankcase pressure due to effects other than the amount of air inducted.